well to test it for oxide of iron, which should be present barely in tracts since clegras containing iron spots the leather. 4. Acid and Saponiacation Numbers.l-These are determined in the usual way on the dry fat from the determination of the non-fatty sub- stances (2).. From the acid number the percentage of free acids expressed as oleic acid (see p. 374) is calculated. 5. Degragene.—This is the special resinous substance formed by the oxidation of the fish or blubber oils l and is what gives body to the de"gras, increases its power of emulsivity with water and renders it specially adapted to the treatment of skins. It is determined as follows 2: 10 grams of the c!6gras, either as it stands or after drying at 100° as indicated under 2 (above), are dissolved together with 7 grams of caustic soda in 10 c.c. of water and 50 c.c. of alcohol, the solution being heated on a water-bath in a reflux apparatus until saponification is complete (about 2 hours). The alcohol is then expelled, the soap dissolved in water and acidified with hydrochloric acid, and the whole boiled until the mixture of fatty acids and degragene becomes quite fluid. When cool, the mass is transferred to a, separating funnel and the flask rinsed out with about 150 c.c. of petroleum ether boiling below 75° ; the whole is well shaken and allowed to stand until the aqueous acid liquid separates sharply from the petroleum solution, the former being then run off. The funnel then con- tains the petroleum ether solution of the fatty acids and of the unsaponifiable substances of the degras, together with an insoluble, blackish, resinous solid constituting the degragene, which adheres well to the walls of the funnel, so that the petroleum solution may be poured from the top of the funnel without any of the degragene being lost. The degragene is then washed with a little petroleum ether and dissolved in hot alcohol, the solu- tion being filtered if necessary, the alcohol evaporated and the residue dried at 160.......105" and weighed. 6. Unsaponiiiable Substances.—According to Baldracco,3 these may be determined exactly as follows;, 15-20 grams of the degras are saponified by boiling with 5 grams of caustic potash dissolved in 10 c.c. of water and 50 c.c. of alcohol for 2-2-| hours in a reflux apparatus, the liquid being then transferred to a dish and the alcohol completely expelled by evaporation on a water-bath. The residue is well mixed with 8 grams of sodium bicarbonate and 50-60 grams of coarse quartz sand previously washed and calcined, and completely dried in an oven at 110°. The mass is then broken into small pieces, placed in an extraction thimble and ex- tracted with petroleum ether boiling below 75°. The petroleum solution is washed several times with water in a separating funnel and then evaporated, the residue, when dried at 110° and weighed, representing the unsaponifiable matter contained in the degras. * The largest proportions of degrugSne are furnished by whale oil and cod-liver oil, which yield, therefore, the best degras. » This is the method proposed by the Committee for the analysis of degras at the Seventh Congress of. the International Association of Leather Trade Chemists, iurin, The other determinations are also those suggested by this Committee. 3 See preceding note.